The present invention relates to a driver for an optical system for horizontally and vertically driving an optical lens or a whole or a part of an optical pickup system including the lens, and more particularly to a driver for an optical pickup system capable of enduring severe external vibration and consuming less power.
A driver for an optical pickup system for recording and/or reproducing optical information in, for example, an optical or magneto-optical disk drive. The optical pickup system records information by focusing the modulated optical beams for scanning a rotating disk. The optical pickup system reproduces the information by scanning the disk with unmodulated light, and detecting modulated optical beams reflected from the disk. In both the record and the playback processes, the disk's mirror face (a recording face) must be in a focal plane, and an optical focus concentrating on the mirror face must precisely trace the center of a track. However, since the recording face is a rough plane and often vibrates in a planar direction due to external vibration and its tilted position, the recording face does not always match the focal plane. Further, when the disk is mounted off-center, the recording face rotates in an elliptical shape and not in a circular shape, which may force the optical focus out of the track's center. As a result, offset focusing and tracking of the optical focus from the track of the disk frequently occur. Therefore, to correct the focusing and tracking offsets, a driver for minutely driving at least a part of the optical pickup system in vertical and horizontal directions is required.
There are disclosed prior art drivers in Japanese laid-open patent publication 1-258236 and Japanese laid-open utility model sho 61-37127. The driver of the former comprises a lens holder having an objective lens of an optical pickup and vertical and horizontal driving coils, a permanent magnet for forming a magnetic field around the driving coils, and a plurality of resilient wires for positioning the neutral position of the lens holder. According to the driver, electromagnetic force created when current flows through the vertical and horizontal driving coils moves the lens holder slightly in a vertical and a horizontal direction, thereby overcoming the elasticity of the resilient wires for holding the lens holder. Here, in order to precisely move the lens holder to a desirable place, the resilient wires must have the same elastic modulus and their own oscillation characteristics must not change under impact. However, since the elastic moduli of the resilient wires tend to have minute differences from one another, the lens holder is distorted and becomes offset when frequent external vibration occurs.
Meanwhile, the driver of the latter having an objective lens mounted at an offset position of the lens holder, for rotating the lens holder on an axis and moving the same in the axis direction. When driving the driving system vertically and horizontally, the moment of inertia due to the mass of the lens holder is unbalanced depending on the position of the objective lens so that the position of the lens holder also changes under minute impacts. Particularly, a counter voltage must always be applied to the vertical driving coil so as to fix the neutral position of the lens holder in the vertical and horizontal directions. This application of the counter voltage consumes a great deal of power.